IEEE 802.11 is a set of media access control (MAC) and physical layer (PHY) specification for implementing wireless local area network (WLAN) communication, in the unlicensed (2.4, 5, and 60 GHz) frequency bands. The standards and amendments provide the basis for wireless network products using the IEEE 802.11 frequency bands. IEEE 802.11 plays an important role in the growing application of Indoor/Outdoor positioning. Direction fining positioning is achieved from either Angle of Departure (AoD) or Angle or Arrival (AoA). In AoD, the transmitter transmits through multiple antennas and the receiver (tracker) resolves the angle of departure relative to the antenna platform of the transmitter based on the received signals. In AoA, the receiver (tracker) employs multiple antennas to receive signal and resolves angle of arrival relative to its own antenna platform orientation. In both AoD and AoA, only one device with multiple antennas or antenna elements is needed, and only one-way signal transmission is required.
Multiple antenna elements on an antenna platform can be used to estimate AoA or AoD based on the phase difference observed from the received signal at the multiple antenna elements or signals received from the multiple antenna elements. However, when the distance between the antenna elements is small, the phase difference is small. It becomes difficult to achieve good angle resolution. In addition, there will be coupling between antenna elements that can affect AoA or AoD accuracy. On the other hand, when the distance between the antenna elements is larger than half a wavelength, the grating lobe occurs and there are multiple solutions to AoA and AoD positioning.
Therefore, it is desirable to increase the distance between the antenna elements beyond half a wavelength to achieve higher resolution for AoA or AoD positioning while eliminating the effects of the grating lobe.